As an individual ages, the eye is less able to accommodate, or bend the natural lens, to focus on objects that are relatively near to the observer. This condition is known as presbyopia. Similarly, for persons who have had their natural lens removed and an intraocular lens inserted as a replacement, the ability to accommodate is absent.
Among the methods used to correct for the eye's failure to accommodate is a method known as mono-vision in which a single vision lens for correction of distance vision is used in the lens wearer's dominant eye and a single vision lens for correction of near vision is used in the non-dominant eye. Monovision is disadvantageous because it results in a loss of stereopsis. Another known method for correction of presbyopia is to use bifocal or multifocal contact lenses in both of the individual's eyes. Use of bifocal or multifocal lenses in both eyes results in a reduction of image contrast and resolution compared to mono-vision. Yet another method of treating presbyopia is to place a bifocal or multifocal lens in one eye and a single vision lens in the other eye. The disadvantage in using this method is in the large number of lenses that must be considered in order to provide the individual with satisfactory lens performance.